1. Field of the Invention
The present invention relates to the technical field of link tubes between the sea floor and a petroleum rig disposed on the sea surface, such floor-to-surface link tubes being used to transport hydrocarbons from the sea floor to the sea surface.
2. Description of the Related Art
Floor-to-surface link tubes can be installed from a petroleum rig out at sea, and can reach a height of 1,000 meters (m) or indeed of 3,000 m. Such floor-to-surface link tubes must thus have particularly high traction strengths in order to withstand not only their own weights but also the torsion and transverse forces exerted by marine currents. In addition, a floor-to-surface link tube installed at a great depth must also withstand the surrounding water pressure.
A first technique consists in installing a transport pipe in a protective riser, also known as a “marine drilling riser”. The space between the riser and the transport pipe can be filled with a thermally insulating gel, or with a heated fluid circulating by being pumped, or it can contain electric trace heating. Thus, the protective marine riser provides thermal protection in order to prevent solidified-hydrate blockages from forming in the transport pipe. In addition, the protective marine riser provides mechanical protection for the transport pipe. The main stress exerted on the transport pipe is stress in traction.
A drawback suffered by the technique of implementing floor-to-surface link tubes by using a protective marine riser is that it is a particularly lengthy technique. Thus, this first technique cannot be used effectively in emergency situations such as, for example, collecting hydrocarbon leaks coming from a subsea well or from equipment installed at great depths.
A second technique consists in using connection and transport pipe segments that withstand open-sea conditions. Each such pipe segment has of its ends threaded and of wider diameter so as to form a junction by quickly screwing together pipe segments placed end-to-end to form a transport pipe installed directly out in the open sea. The reinforced and threaded male or female ends are also referred to as “tool joints”. The mechanical characteristics of such pipe segments enable the pipe installed directly out in the open sea to withstand not only traction forces but also the torsion and transverse forces exerted by the marine currents. Regarding its thermally protection, the transport pipe installed directly out in the open sea is equipped with a thermally insulating material held around the pipe by a sheath made of a plastics material.
However, a drawback is that such second assembly technique does not make it possible to provide thermal insulation that is effective. Thus, irreversible stoppages can occur due to formation of blockages of paraffin or of methane hydrate. The lower the temperature of the subsea hydrocarbon well and the deeper the floor-to-surface link tubes goes, the more frequent that type of failure is, since the floor-to-surface link tube then suffers major heat losses.